(1) The 14C-2-deoxy-D-glucose method (Sokoloff et al., 1977) was used to study regional cerebral glucose metabolism as a function of age in Fisher 344 rats (3, 12 and 24 mo. animals). Structures which showed no significant decrements with age were cerebellar gray and white matter, nucleus accumbens, septum, hypothalamus and thalamus. Structures which showed reductions, of the order of 20-30%, were superior colliculus, inferior colliculus, medulla, midbrain, caudate nucleus, frontal and lateral cortex. Most changes occurred between 3 and 12 months of age rather than between 12 and 24 months, and probably reflect age-related altered functional states of the affected brain regions. (2) Cerebral glucose utilization in rats markedly increased in most areas of the cerebral cortex and declined in many subcortical structures during spreading cortical depression. Cortical glucose utilization remained elevated during recovery, and was distributed in perpendicular cortical columns. (3) 14C-iodoantipyrine provided better measures of regional cerebral blood flow than did 14C-antipyrine in conscious rats. 3H-nicotine also could be employed to measure regional cerebral blood flow accurately.